Machsupport Forum
Mach Discussion => General Mach Discussion => Topic started by: beefy on May 08, 2013, 05:18:07 AM
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My cam software for my plasma cutter gives me the following code as part of the touch of sequence:
G28.1 Z15 F500
From safe Z my torch rapids down to 15 mm then travels to the home switch at a reduced feedrate. What I am not sure of is whether it will be using the F500 code or it will be using the % speed setting in Config/Homing Limits. I assumed having the F500 in the line of code would OVERIDE the % setting in Config/Homing Limits.
Someone has told me that in the code above the F500 is redundant because it only comes into play IF there is a G1, G2 or G3 in the line of code. IS THIS TRUE ?? That's my big question.
Googling Mach & G28.1 a description of G28.1 was that it causes a homing move at a % (set in Config/Homing Limits) of the CURRENT feedrate. If that's true then doesn't that mean the homing speed will change depending on what the current feedrate is. I always though the homing % speed setting was a percent of rapid speed and would always be the same.
I'm hoping the F500 command in the line of code will overide the % setting so my homing speed is consistent regardless of the current feedrate.
Cheers,
Keith.
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Keith - on my system (R3.043.022) the behavior of G28.1 is not as described in the gcode reference.
The first phase of G28.1 is at rapid and the second phase is at the % of rapid as set in Homing/Limits
i.e. Feedrate is ignored regardless of whether it precedes or is on the same line as the G28.1.
Ian
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Thanks Ian,
I'll have to write a tiny bit of code to try it on my table.
If that's the case it seems like a pointless exercise to put this referencing speed setting in my post processor, plus homing speed is not constant and is a percentage of current feedrate. Interesting, I would have thought a machines homing speed would be a fixed value, not connected to current feedrate.
Cheers,
Keith.
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I think I'm getting to the bottom of the rabbit hole on learning about G28.1
Homing is done at a % of CURRENT FEEDRATE, as set in Config/Homing Limits
When my plasma table Z axis does its very FIRST touch off operation, the only feedrate command that has been given before this is F1 which is 1mm/min in my case. Now I know that my first Z homing operation is not done at a the % setting of 1 mm/min. There are however some G0 command before the first touch off so my question is does a G0 command set the current feedrate to the rapid speed, and therefore my homing speed gets done at a % of the rapid speed.
Or in summary, is the following true:
F1234 in first line of code - current feedrate is now 1234 mm/min
G0 in second line of code - current feedrate is now machines rapid speed
Cheers,
Keith.
EDIT: Topics merged by Mod
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Hi Keith - Can I ask you to read my first reply again? - It appears you're confusing and interchanging RAPIDs and FEEDRATE moves here and there throughout your last two replies.
Cheers
Ian
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Hi Ian,
yes I was, thanks for the correction.
Cheers,
Keith.